KVM: x86: document special identity map address value

Setting it to 0 leads to setting it to the default value, let's document
this.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
1 file changed